Remove superfluous HYDRA_LOGO environment variable

Dependencies

• [2] R6APT7HG Fix hydra_logo setting
• [3] 6KJXJB7N qualify ordery_by clauses when necessary, remove unnecessary order_by's, reported by Ludo, resulted in errors in sqlite
• [4] AFEKITYD Fix some warnings about undefined values
• [5] XJRJ4J7M Add user registration
• [6] X5BWNTMA Make the logo configurable via hydra.conf
• [7] IZEXRZWT Replace old logo with Nix/NixOS logo.
• [8] EFWN7JBV * Added a status page that shows all the currently executing build steps.
• [9] MVB7RRLT * Move NARs from the NixChannel controller to the Root controller and
• [10] HRAFVVOE make logo configurable via HYDRA_LOGO env var
• [11] G4X5IUYJ Remove default logo, replaced by text for now. Hide template in jobset edit.
• [*] J5UVLXOK * Start of a basic Catalyst web interface.

Change contents

• replacement in src/lib/Hydra/Controller/Root.pm at line 33
  [3.134]→[2.0:89](∅→∅)
  − $c->stash->{logo} = ($c->config->{hydra_logo} // $ENV{"HYDRA_LOGO"}) ? "/logo" : "";
  [3.134]

  [3.40]
  + $c->stash->{logo} = defined $c->config->{hydra_logo} ? "/logo" : "";
• replacement in src/lib/Hydra/Controller/Root.pm at line 273
  [3.323]→[2.90:177](∅→∅)
  − my $path = $c->config->{hydra_logo} // $ENV{"HYDRA_LOGO"} // die("Logo not set!");
  [3.323]

  [3.382]
  + my $path = $c->config->{hydra_logo} // die("Logo not set!");